Thai marines killed 16 insurgents who launched an attack on a military base in the country's south, authorities said. It is believed to be the deadliest toll of Islamist fighters since more than 100 died in a single day nearly a decade ago.

About 50 militants wearing combat uniforms raided the marine corps base in the Bacho district of Narathiwat province late on Tuesday night, Colonel Pramote Promin said.

The shootout ended with at least 16 militants killed and the rest fleeing, Pramote said, adding that soldiers suffered no casualties. He said the marines had been tipped off by local people beforehand.

Regional army commander Lieutenant Udomchai Thammasaroraj said in an interview on ThaiPBS channel that the army had declared a curfew for the area within three miles (5km) of the base on Wednesday night.

An Islamic insurgency erupted in 2004 in Thailand's three southernmost provinces, a Muslim-majority region in the Buddhist-dominated country. In April that year guerrillas launched simultaneous attacks on police stations and checkpoints, triggering clashes in which more than 100 militants died; 32 of them were killed at the Kreu-Sae mosque in Pattani.

Sunai Phasuk, a Bangkok-based researcher for Human Rights Watch, said: "The insurgents were uplifted because of a surge in their successful attacks in recent weeks, so this is a significant loss on their side. From now authorities will certainly have to be very concerned about their retaliation."

He said Narathiwat province was a contested area between security forces and militants.

Muslims in the south have long complained of discrimination by the central government in the capital, Bangkok, and the insurgents are thought to be fighting for autonomy. But the insurgency itself remains murky, with militants making no public pronouncements on their goals.

Fighting in the area is reported on a near-daily basis and more than 5,000 people have been killed. Security forces, as well as teachers, have been targeted by insurgents because they are seen as representatives of the government.

On Sunday, suspected militants killed five soldiers and wounded five others in two attacks, including a car bombing in Yala province that happened as a truck carrying six soldiers passed. The militants then opened fire on the soldiers, killing five, and took away the dead soldiers' rifles, it was reported.

Officials from security agencies were scheduled to meet on Friday to discuss safety measures for the southernmost provinces.